.

wcfs/internal/xbtree/δbtail.go

@@ -62,10 +62,11 @@ package xbtree
 //
 // Queries are relatively straightforward code that work on vδT snapshot. The
 // main complexity, besides BTree-diff algorithm, lies in recomputing vδT when
-// set of tracked keys changes.  XXX and in concurrency
+// set of tracked keys changes and in handling that recomputation in such a way
+// that multiple Track and queries requests could be all served in parallel.
 //
 //
-// XXX concurrency
+// Concurrency
 //
 // trackSet, ktrackNew, krebuildJobs + explain rebuild algo (query lock, check ktrackNew, krebuildJob, go/merge/...)
 //
@@ -373,7 +374,8 @@ func nodePathToPath(nodePath []Node) (path []zodb.Oid) {
 }
 
 func (δBtail *ΔBtail) track(path []zodb.Oid, keycov KeyRange) {
-	// XXX locking
+	δBtail.mu.Lock() // TODO verify that there is no in-progress writers
+	defer δBtail.mu.Unlock()
 
 	if traceΔBtail {
 		pathv := []string{}